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Documentation / input / walkera0701.txt




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Based on kernel version 3.13. Page generated on 2014-01-20 22:03 EST.

1	
2	Walkera WK-0701 transmitter is supplied with a ready to fly Walkera
3	helicopters such as HM36, HM37, HM60. The walkera0701 module enables to use
4	this transmitter as joystick
5	
6	Devel homepage and download:
7	http://zub.fei.tuke.sk/walkera-wk0701/
8	
9	or use cogito:
10	cg-clone http://zub.fei.tuke.sk/GIT/walkera0701-joystick
11	
12	
13	Connecting to PC:
14	
15	At back side of transmitter S-video connector can be found. Modulation
16	pulses from processor to HF part can be found at pin 2 of this connector,
17	pin 3 is GND. Between pin 3 and CPU 5k6 resistor can be found. To get
18	modulation pulses to PC, signal pulses must be amplified.
19	
20	Cable: (walkera TX to parport)
21	
22	Walkera WK-0701 TX S-VIDEO connector:
23	 (back side of TX)
24	     __   __              S-video:                                  canon25
25	    /  |_|  \             pin 2 (signal)              NPN           parport
26	   / O 4 3 O \            pin 3 (GND)        LED        ________________  10 ACK
27	  ( O 2   1 O )                                         | C
28	   \   ___   /      2 ________________________|\|_____|/
29	    | [___] |                                 |/|   B |\
30	     -------        3 __________________________________|________________ 25 GND
31	                                                          E
32	
33	
34	I use green LED and BC109 NPN transistor.
35	
36	Software:
37	
38	Build kernel with walkera0701 module. Module walkera0701 need exclusive
39	access to parport, modules like lp must be unloaded before loading
40	walkera0701 module, check dmesg for error messages. Connect TX to PC by
41	cable and run jstest /dev/input/js0 to see values from TX. If no value can
42	be changed by TX "joystick", check output from /proc/interrupts. Value for
43	(usually irq7) parport must increase if TX is on.
44	
45	
46	
47	Technical details:
48	
49	Driver use interrupt from parport ACK input bit to measure pulse length
50	using hrtimers.
51	
52	Frame format:
53	Based on walkera WK-0701 PCM Format description by Shaul Eizikovich.
54	(downloaded from http://www.smartpropoplus.com/Docs/Walkera_Wk-0701_PCM.pdf)
55	
56	Signal pulses:
57	                   (ANALOG)
58	    SYNC      BIN   OCT
59	  +---------+      +------+
60	  |         |      |      |
61	--+         +------+      +---
62	
63	Frame:
64	 SYNC , BIN1, OCT1, BIN2, OCT2 ... BIN24, OCT24, BIN25, next frame SYNC ..
65	
66	pulse length:
67	   Binary values:		Analog octal values:
68	
69	   288 uS Binary 0		318 uS       000
70	   438 uS Binary 1		398 uS       001
71					478 uS       010
72					558 uS       011
73					638 uS       100
74	  1306 uS SYNC			718 uS       101
75					798 uS       110
76					878 uS       111
77	
78	24 bin+oct values + 1 bin value = 24*4+1 bits  = 97 bits
79	
80	(Warning, pulses on ACK are inverted by transistor, irq is raised up on sync
81	to bin change or octal value to bin change).
82	
83	Binary data representations:
84	
85	One binary and octal value can be grouped to nibble. 24 nibbles + one binary
86	values can be sampled between sync pulses.
87	
88	Values for first four channels (analog joystick values) can be found in
89	first 10 nibbles. Analog value is represented by one sign bit and 9 bit
90	absolute binary value. (10 bits per channel). Next nibble is checksum for
91	first ten nibbles.
92	
93	Next nibbles 12 .. 21 represents four channels (not all channels can be
94	directly controlled from TX). Binary representations ar the same as in first
95	four channels. In nibbles 22 and 23 is a special magic number. Nibble 24 is
96	checksum for nibbles 12..23.
97	
98	After last octal value for nibble 24 and next sync pulse one additional
99	binary value can be sampled. This bit and magic number is not used in
100	software driver. Some details about this magic numbers can be found in
101	Walkera_Wk-0701_PCM.pdf.
102	
103	Checksum calculation:
104	
105	Summary of octal values in nibbles must be same as octal value in checksum
106	nibble (only first 3 bits are used). Binary value for checksum nibble is
107	calculated by sum of binary values in checked nibbles + sum of octal values
108	in checked nibbles divided by 8. Only bit 0 of this sum is used.
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